For manufacturing a 3-isochromanone represented by the later described formula (II), some different methods have been proposed. For example, JP-A-9-67364 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a method of reacting .alpha.,.alpha.'-dihalogeno-o-xylene with carbon monoxide and water in the presence of a hydrogen halogenide scavenger and a-complex catalyst containing a metal such as palladium. Furthermore, A. Cowell et al have reported that 3-isochromanone is synthesized by reacting o-bromomethylbenzyl alcohol with carbon monoxide in the presence of a palladium complex catalyst (JACS., 102, 4191 (1980)).
Also, in some methods hitherto proposed, 3-isochromanone is synthesized by the Baeyer-Villiger oxidation reaction using 2-indanone as a starting material. More specifically, A. Chatterjee et al, P. Cottet et al and C. Kocch et al disclose a method of synthesizing 3-isochromanone by reacting 2-isodandne with a metachloroperbenzoic acid (see, Synthesis, 818 (1981), Synthesis, 497 (1987), Synthetic Communication, 19, 829 (1989)). F. G. Mann et al disclose a method of synthesizing 3-isochromanone by reacting .alpha.-methoxy-.alpha.'-cyano-o-xylene in an aqueous sulfuric acid solution (see, J. Chem. Soc., 2819 (1954)). Furthermore, U. Azzena et al disclose a method of synthesizing 3-isochromanone by ring-opening phthalan with a metal lithium, reacting it with carbon dioxide and hydrolyzing the reaction product (see, Tetrahedron Lett., 36, 8123 (1995)).
However, these methods are not an industrially useful method because the starting materials are difficult to be synthesized and prevented from the industrial use for general purposes, an expensive reagent or catalyst is necessary to be used or the yield is low.